The present invention relates to an internal combustion engine stroke identification system, particularly for application on a sequential, timed electronic injection system.
Electronic injection systems on internal combustion engines are known to present an electronic control system which, depending on the signals received from various sensors (mainly engine speed/stroke and intake air pressure/temperature sensors), determines, for example, air density inside the manifold and engine speed, and calculates, via interpolation on respective memorised maps, the stroke and timing for injecting fuel into the injectors, as well as the spark lead. Provision may be made for one injector per cylinder, located downstream from the throttle valve, or for a single injector located up- or downstream from the throttle valve. Such a sequential, timed electronic injection system therefore employs a given number of angular references on the drive and distributor shafts, for enabling the control system to determine the stroke (induction, compression, expansion, exhaust) of each cylinder. Each half revolution of the engine, the control system is therefore able to open the specific injector relative to the cylinder performing the required stroke. The engine strokes, however, must be identified by the control system within the shortest possible time after starting, for enabling correct fuel supply as soon as the engine is started up.
Use is generally made of a first sensor facing a pulley angularly integral with the drive shaft, the said pulley having four projecting teeth equally spaced at 90.degree. intervals, and a pair of sensors facing a cam secured angularly to the distribution shaft, which cam presents a pair of teeth spaced 90.degree. apart. The said pair of sensors, however, presents a number of drawbacks, due to possible interference between the respective magnetic circuits, particularly if the system is fitted onto existing distributors not specifically designed for the purpose, thus resulting in interference signals and false signaling of the said sensors.